Digital cameras have become small and inexpensive, and as a result, many electronic devices can include a digital camera. Examples of such electronic devices include many portable wireless electronic devices, such as cellular telephones, smart phones, tablet computers, laptop computers, and the like. These cameras can be convenient additions to electronic devices because the cameras are often portable enough to be carried with the user at most times. The camera in a portable device can be used for taking pictures and videos to document events and communicate with others. The camera can also be used as a data entry or data capture device, where the camera can be configured to scan documents and various types of bar codes. As computer processing power and storage capacity in portable electronic devices increases with improved technology, cameras can be used to capture vast amounts of image data (e.g., still photos and moving video images) and process, store, and communicate such data for many useful purposes.
A digital camera includes a lens that focuses light from objects in a scene on a light sensor or image sensor. The sensor can convert the light, at each pixel location on the sensor, into digital data. Although light beams or rays from all the objects in a scene can reach the image sensor, all light rays may not be in sharp focus on the sensor. In optics, depth of field (DoF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in a captured image. The DoF is determined by the camera-to-subject distance, the lens focal length, the lens f-number (i.e., the lens opening), and the format size or circle of confusion criterion. The f-number is the focal length divided by the “effective” aperture diameter. Thus, the size of the opening in the aperture of the camera can be a compromise between allowing more light onto the sensor and sharply focusing the light from a wide range of distances between the camera lens and the objects being photographed.
Some cameras used in electronic devices use a focusing system referred to as an autofocus system. An autofocus system uses a motor to position the lens so that rays incident on a portion of the sensor can be brought into focus. Rays from other objects in the scene may or may not be suitably focused, depending upon the depth of field of the camera settings and the distances of the objects to the lens.
Another type of camera used in electronic devices uses a fixed focus system. The fixed focus system does not move the lens to focus the image on the sensor. Instead, an image is focused on the sensor by designing a lens configuration that attempts to bring many of the objects in the scene into focus (i.e., a configuration with a large DoF) without making the lens aperture too small, and thus making the camera too slow to capture an image. In other words, the fixed focus camera relies on sufficient depth of field to produce acceptably sharp images. The advantage of the fixed focus design is that it can be produced very inexpensively, more so than autofocus or manual focus systems. It is also reliable because it lacks moving parts. It can also be faster and easier to use. The system is effectively automatic; the photographer need not worry about focusing. It can also be more predictable than autofocus systems.
There are now various software algorithms and techniques that can be used to extend the DoF of a fixed focus camera and make it possible to increase or extend the depth of field by analyzing and processing the data captured in a digital image. By properly profiling the lens and image sensor configuration, software algorithms can be used to restore focus to blurred images by reconstructing light rays corresponding to blurred portions of a captured image.
It is in view of this background information related to the design and use of a camera in an electronic device that the significant improvements of the present disclosure have evolved.